Belief in God is rational.
Everything has a cause. So unless there is a first cause, then you would have an infinite regress. And then nothing could exist. Therefore there must be a first cause. Therefore God, the first cause, exists. QED. (You could prove the first step a priori that everything has a cause by noting that nothing can come from nothing. This makes it a priori, not just an empirical observation).

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22.2.16

To some degree our own souls and the souls of others are hidden. But there is a surprisingly easy way of seeing the state of any person's soul. See what they talk about when they are relaxing among friends. If they are not on guard but just relaxing and chatting their essence, their inner desires because expressed in words. And you can see the same for groups. When you walk into the place where they gather either to learn or talk, what do they talk about? This shows their inner state. Then you can see if their noble flowery words about what they do and think match the true reality.

If their conversation is all about how to get secular Jews to give them money and what is wrong with secular Jews then you know you are not dealing with an elevated spiritual community. Even if they insist on how spiritual they are, you already have a guarantee measuring stick. You can see if the claims are the same as the facts. You can see if they are just some cult around a leader, or if they are into Torah. You can see if they are building a cult based on the lie that they are all about Torah while in fact building their power base.

For this reason I have suggested that people learn only in Litvak yeshivas because only in such places have I seen the words match the facts.